This publication invites you to discover the multiple facets of a collaborative city from A-Z, based on our over 25 years’experience of what works well in Europe.The list is, of course, not exhaustive as the beauty of energy transition is the wide and unlimited field of possibilities that it opens up! What it is proposing however is a change of perspective. As the energy landscape is undergoing radical change, from a once hierarchical and monopolistic system to a more distributed and decentralised one, so too should the decision-making architecture. Indeed, a new system cannot be designed using outdated models: in writing a new chapter of our history, we must also empower its new stakeholders. We, the local and regional actors, are these new players, through the role we play in mobilizing civil society and SMEs, tapping into the large array of dispersed renewable or locally recovered energy sources and increasing energy savings and efficiency through ambitious building, urban planning and mobility strategies. This publication complements Energy Cities’ “30 proposals for the energy transition of cities” with its many case studies.